The Pozzolan Activity of Calcined Kaolin in Concrete

  • Friday, 13 January 2023
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The Pozzolan Activity of Calcined Kaolin in Concrete

Kaolin is a mineral that is a major component in the ceramic industry.calcined kaolin It is found in coated paper, cosmetics and toothpaste. This white-firing material is also used in the manufacture of sanitaryware. The kaolin mineral is composed of 50% quartz and limestone in a 2:1 ratio. In addition, it contains a pozzolanic activity.

The pozzolan activity of calcined clays depends on the calcination temperature, its degree of order, the kaolinite content and the surface after grinding.calcined kaolin Although the most important factor shaping the calcined clay's pozzolan activity is its kaolinite content, the dehydroxylation of kaolinite is also an important parameter. The dehydroxylation of kaolinite occurs at 650 degC.

A study on the effect of iron nitrate on the pozzolanic activity of calcined kaolin showed that iron ions have less favourable effects on the clay. Iron ions in the clay prefer to stay within the own layer, rather than migrate to the surface. However, this does not mean that the presence of iron ions has no influence on the material. To improve the pozzolan activity, Ghorbel and Samet added an iron nitrate solution to the clay, which formed hematite. They did not use more than 2.7% of this admixture.

In order to evaluate the effect of the calcination process on the concrete, the authors made two series of concrete. One series contained general purpose cement, while the other was comprised of Type I cement. Both were subjected to a calcination in a rotary kiln. After calcination, both concretes were characterized by their strength performance and workability. But, the results were largely inconclusive.

One method to determine the kaolinite content of the calcined kaolin was the Chapelle test. By boiling the sample in calcium hydroxide for 16 hours, it was possible to assess the Ca(OH)2 content in the filtrate. This quotient was called the P0 coefficient. High P0 values indicate a well-organized structure, while low values indicate disorder. As a result, the strength of the mortars depended on the inverse of the P0 coefficient.

Some studies have investigated the effect of the calcination temperature on the pozzolanic activity of the calcined clay. A study by Ferreiro and coworkers examined the effect of calcination at two different temperatures. They compared the properties of the LC3 based on a mixture of two types of clay, one with a high kaolinite content, and another with a low kaolinite content. Their results showed that the LC3 mortar with 30% kaolinite showed a higher strength than the control mortar.

Another study evaluated the carbonation resistance of LC3. For this purpose, the authors created a series of concrete with different aggregate, water, binder and kaolin content. These were then compared with a control series that included a mixture of pure cement and a calcined kaolin. Their findings suggested that LC3 mortars were more resistant to carbonation than those with OPC.

However, these results have not been thoroughly investigated. There is a need to understand more about the properties of the different clays that are used in the production of calcined kaolin.

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